New Zealand lies on the boundary of two continental plates and has been isolated by oceanic barriers for the last 60 – 80 million years. The Southern Alps formed as a result of the movement between these two plates over the last five million years. The rise of the Alps changed the weather patterns, resulting in the west coast of the South Island being much wetter than the east coast. The uplift of the Alps also changed the soils in the regions. Between 1.6 million years ago and 10 000 years ago New Zealand was exposed to, and affected by, cold glacial and warmer interglacial periods. These caused the sea levels to fluctuate by up to 135 metres. In the glacial periods, forests retreated from the mountains towards the coasts. Hebe species are found throughout the country, particularly on the banks of lowland streams and rivers and in the alpine (above the treeline) and subalpine zones of the mountains. It has been proposed that the ancestral form of the current Hebe species arrived as a single introduction, most likely from Australia, about five million years ago. The closest modern species to this ancestor is thought to be H. cupressoides. The patterns of diversifi cation of the Hebe species suggest a rapid radiation following establishment. The ancient founder population that gave rise to the Hebe complex in New Zealand was most likely small, and perhaps arose from a single seed. The initial populations were later fragmented by changing sea levels, mountain building and glaciation. The combined influences of inbreeding, genetic drift and strong selection acting on small populations have probably played a major role in the rapid diversification of the Hebe species. Chromosomal changes related to aneuploidy and polyploidy have also been observed. H. cupressoides H. ochracea H. cheesemanii Examples of whipcord forms
H. elliptica H. salicifolia Examples of larger leaf forms
Five different species of Hebe showing diversity in morphology.
Species
Habitat conditions
Morphology
Chromosome number (n)
H. cupressoides
Subalpine east of the main mountains of the South Island.
Whipcord plant with scale-like leaves that grows up to 2 m tall.
21
H. cheesemanii
Rocks on drier mountains of the South Island.
Semi-whipcord plant; shrub up to 0.3 m tall.
21
H. ochracea
Mountains of the north-west South Island.
Semi-whipcord plant; shrub up to 0.3 m tall.
62
H. hectorii
Wet subalpine scrub and tussock of the South Island.
Whipcord plant; erect, rigid plant that grows up to 0.75 m tall.
20
H. imbricata
Drier mountains of the South Island.
Whipcord plant; erect, much branched rounded shrub up to 0.6 m tall
20
H. salicifolia
Lowland to mountains in the South Island; widespread except near the coast in Marlborough Sounds.
Leaves 5 – 15 cm long; shrub up to 5 m tall.
20
H. speciosa
Exposed sea cliffs on western side of both main islands.
Leaves 5 – 10 cm long; rounded shrub up to 2 m tall.
20
H. cockayniana
Wet subalpine scrubland and grasslands in south-west South Island.
Leaves 1 – 2 cm long; erect much branched shrub up to 1 m tall.
20
H. elliptica
Coastal.
Leaves 1.5 – 4 cm long; bushy shrub up to 2 m tall.
20
H. topiaria
Wet subalpine areas of the South Island.
Leaves about 1 cm long; compact neatly rounded bushy shrub up to 2 m tall.
61
H. gracillima
Damp swampy places in the South Island.
Leaves 1 – 2 cm long; shrub up to 2 m tall.
40
H. venustula
Subalpine mostly North Island
Leaves 1 – 2 cm long; erect bushy shrub up to 1.5 m tall.
60
H. stricta
Common in lowland and subalpine areas, mostly on banks in the North Island.
Leaves 4 – 5 cm long; woody shrub up to 4 m tall.
20
H. odora
Common usually in wet ground, alpine and subalpine.
Leaves 1 – 2 cm long; variable shrub up to 1.5 m tall.
21
H. haastii
Drier mountains of the South Island
Leaves 0.6 – 1.3 cm long; very low growing shrub up to 0.3 m tall
21
H. societatis
Subalpine small plant zone in northwest South Island.
Leaves 1 – 2.5 cm long; subshrub that grows up to 0.3 m tall.
21
H. crenulata
Subalpine shrubland and tussock grassland, often in shallow or rocky soils of northern South Island.
Leaves 0.6 – 1.9 cm long; spreading low shrub up to 1 m tall.
40
H. dilatata
Grasslands to rocky screes of southern South Island.
Leaves 1 – 2.5 cm long; subshrub that grows up to 0.3 m tall.
60
H. raoulii
Drier mountains and hills of the South Island.
Leaves 0.6 – 2.5 cm long; small low growing shrub up to 0.3 m tall.
21
Table 1 Summary of characteristics of key Hebe species
Discuss the evidence for the role of each of the following in the evolution and diversifi cation of the Hebe species in New Zealand: • selection pressures generated by environmental changes resulting from mountain building and glaciation • mutations, particularly aneuploidy and / or polyploidy • genetic drift and / or the Founder effect • adaptive radiation and / or convergence • sympatric and / or allopatric speciation. Your answer needs to address all the bullet points. Where there are two concepts for one bullet point it is not essential that both concepts are covered. Headings may be used.
New Zealand lies on the boundary of two continental plates and has been isolated by oceanic barriers for the last 60 – 80 million years. The Southern Alps formed as a result of the movement between these two plates over the last five million years. The rise of the Alps changed the weather patterns, resulting in the west coast of the South Island being much wetter than the east coast. The uplift of the Alps also changed the soils in the regions.
Between 1.6 million years ago and 10 000 years ago New Zealand was exposed to, and affected by, cold glacial and warmer interglacial periods. These caused the sea levels to fluctuate by up to 135 metres. In the glacial periods, forests retreated from the mountains towards the coasts.
Hebe species are found throughout the country, particularly on the banks of lowland streams and rivers and in the alpine (above the treeline) and subalpine zones of the mountains.
It has been proposed that the ancestral form of the current Hebe species arrived as a single introduction, most likely from Australia, about five million years ago. The closest modern species to this ancestor is thought to be H. cupressoides. The patterns of diversifi cation of the Hebe species suggest a rapid radiation following establishment. The ancient founder population that gave rise to the Hebe complex in New Zealand was most likely small, and
perhaps arose from a single seed. The initial populations were later fragmented by changing sea levels, mountain building and glaciation.
The combined influences of inbreeding, genetic drift and strong selection acting on small populations have probably played a major role in the rapid diversification of the Hebe species. Chromosomal changes related to aneuploidy and polyploidy have also been observed.
H. cupressoides H. ochracea H. cheesemanii
Examples of whipcord forms
H. elliptica H. salicifolia
Examples of larger leaf forms
Five different species of Hebe showing diversity in morphology.
of the South Island.
that grows up to 2 m tall.
rounded shrub up to 0.6 m tall
both main islands.
up to 2 m tall.
tall.
Island.
South Island.
soils of northern South Island.
South Island.
Table 1 Summary of characteristics of key Hebe species
Discuss the evidence for the role of each of the following in the evolution and diversifi cation of the Hebe species in New Zealand:
• selection pressures generated by environmental changes resulting from mountain building and glaciation
• mutations, particularly aneuploidy and / or polyploidy
• genetic drift and / or the Founder effect
• adaptive radiation and / or convergence
• sympatric and / or allopatric speciation.
Your answer needs to address all the bullet points. Where there are two concepts for one bullet point it is not essential that both concepts are covered. Headings may be used.